Self cooling blast pad



Sept. 25, 1962 Y. PETESON 3,055,176

SELF COOLING BLAST FAD Filed Dec. 28, 1960 INVENTOR. l YORK PTERSO/V United States Patent M 3,055,176 SELF COOLING BLAST PAD York Peterson, 308 Canon Drive, Santa Barbara, Calif. Filed Dec. 28, 1960, Ser. No. 79,010 7 Claims. (Cl. (iO-39.09)

My invention relates to the testing of jet engines, and has particular reference to a self cooling blast pad which withstands continued use without deterioration.

.Tet engines are invariably tested in test cells prior to installation on an aircraft, These engines are mounted in the cell fairly close to the ground. As a result, the blast of hot gases from the exhaust (the jet) deteriorates ordinary materials quite rapidly, exposing bare earth which blows away, creating a dust problem. Invariably blast fences are disposed at some distance from the cell to deflect the jet upwardly and break up some of the intense noise which otherwise disturbs the countryside.

Various materials have been used from time to time as blast pads for these test cells in an attempt to nd a material that would withstand operation of a jet engine during test. Ordinary vrock and concrete exfoliate upon use because of the intense heat. Various attempts have been made to cool the material of the blast pad. For example, streams of water'have been continuously directed on such blast pads but with very littlel lessening of their deterioration. While some types of materials will withstand lthese blasts, they are so expensive as to be impractical from a construction standpoint.

I have discovered that ordinary atmospheric air may be used as an effective coolant for test pads. I have discovered furthermore that the action of the blast itself may be used as a pump or a power source for directing the air over the surface of the blast pad. My invention makes it possible to use ordinary construction concrete as a material for a blast pad.

It is therefore a general object of my invention to provide an inexpensive blast pad for jet engines and the like which withstands repeated use without deterioration.

Another object of -my invention is to provide a self cooling blast pad employing atmospheric air as the cooling medium.

A further object of my invention is to employ theenergy of the blast itself to direct a coolant over a blast pad.

A further object is to provide a self cooling blast pad made of ordinary construction materials, and by ordinary construction techniques.

Other objects and advantages of my invention willbe apparent in the following description and claims considered together with the accompanying drawings in which:

FIG. 1 is an elevation view of a blast pad embodying my invention receiving the blast from a test cell.

FIG. 2 is a plan view of the blast pad of FIG. l.

FIG. 3`is a sectional'view on an enlarged scale of the blast pad of FIG. 2 taken along the line III-III of FIG. 2.

FIG. 4 is an enlarged fragmentary sectional view taken along the line IV-IV of FIG. 2.

Referring to FIGS. l and 2, a test cell may be mounted on suitable supports 11 `and may hold a jet engine (not shown) which under test will direct a blast A12 of hot gases toward the left of FIG. l. These engines are generally so mounted that their blast is horizontal and the axis of this blastmay be designated generally by the line 13. Where this blast lstrikes the ground there is provided a blast pad 14 constructed particularly in accordance with the invention. This blast pad 14 may be a slab 16 of concrete or similar construction materials preferably having a curb 17 illustrated best in FIG. 3, and having a series of transverse slots 18. The end toward the test cell 10 is called the forward end of the pad and is designated .concrete on the downstream side of the slot 18.

y 3,055,176 Patented Sept. 25, 1962 ICC- 2 by the numeral 19. The exterior edges are designated by the numeral 21.

It will be observed particularly in FIG. 3 that the top of the slab 16 may be generally level with the top of the joining ground 22. Along each of the exterior edges 21 there is formed an air channel 23 by surfacing an inclined ditch 24 with rock or similar materials.

The slots 18 are shaped particularly in accordance with the invention and their detailed construction is shown particularly in FIG. 4. Each slot 18 has a leading edge 26 which-is the edge toward the test cell 10 or towards the front 19 of the slab 16. Each slot 18 has a trailing edge 27 which is on the downstream side of the blast 12 indicated by the arrow in FIG. 4. Thev leading edge 26 is higher by dimension h than the-trailing edge 27. The width of the'slot 18 is designated by the letter w. -I have discovered that this use of a leading edgewhich is closer to the jet axis than the trailing edge creates a turbulence or aspiration which sucks atmospheric air out of the slot 18 causing it to flow in a thin boundarylayer over the It is this film of cool atmospheric air which insulates the concrete slab 16 from the heat of the blast 12. This insulation of cool air protects the concrete so that it does not exfoliate and disintegrate with use.

The number of transverse slots 18 depends, of course, upon the intensity of the heat. The cool Iboundary layer is, of course, rapidly heated by the intense temperatures of the blast 12. and when this air becomes so heated that it is likely to cause deterioration then another slot must be provided to bring in kadditional air at that point.

EIn testing a standard type of jet engine, I have found that a blast pad of 45 feet in length may be cooled by about 15 transverse slots. These slots toward the test cell -10 are preferably closer together because the exhaust gases vare hotter closer to the test cell and are less dispersed.

I have discovered that the difference in level (distance 4from the blast axis) between the leading and trailing edges of lche slots 18 can be expressed as a function of the width of the slots. Accordingly, with reference to FIG. 4, the dimension h should be not less than one-eighth of the width w. -In practice I prefer to use the ratio of one to six and have found, for example, that a dimension h of one-half inch may be employed in a slot having a width of three inches. The ramp or incline leading up to the dimension h was six inches in'this particular illustration. In view of the great velocity of the' blast 12, this slight ratio of one to eight is elective. For slower velocities of hot gases, the ratios, of course, can be a larger fraction.

Also, if the blast is hotter then 'the ratio should be a i larger Ifraction.

It will be noted particularly with reference to FIGS. 3 and 4 that the depth of the slots 18 may vary, being greater at the external edge 2.1 than towards the middle'of the slab 16. This, of course, is desirable because of the utilization of the air as it progresses from the edge toward the middle. In practice I .prefer to have a minimum slot depth at the center that is greater than the width of the slot. Depth at the external edge may be twice that towards the middle.

As shown best in FIG. 3, the air channel 23 creates a collection place for cool vatmospheric air and the definition of the channel 23 and its separation from the blast of the jet may be enhanced by the provision of the curb 17. In practice I have found that a simple curb six inches high is satisfactory for a ditch depth of approximately a foot. Where it is not practical to obtain cool air from `the atmosphere immediately adjacent the blast pad, this air can, of course, be supplied by the pipes or other suitable conduits, but preferably having air under pressure.

While I have described my invention with respect to a specific embodiment thereof, I do not limit myself to this embodiment. For example, it may be possible to utilize the same etect as a blast pad for rockets. In this event, a pyramid would be formed wherein the inclined surface would be provided with slots in accordance with the invention and preferably atmospheric air would be supplied under pressure by ducts. The rocket blast would in this event be located at the apex of the pyramid. In this event also the slab would be inclined to the jet axis. Other modifications and variations of my invention will be apparent to those skilled in the Iart and accordingly I claim all such modifications and variations that come within the true spirit Iand scope of -my invention.

I claim:

1. A self cooling blast pad for heat-engines mounted at one end of the pad comprising: a slab having a surface disposed generally parallel to Vthe axis of the blast from the heat engines; a plurality of slots in the surface of said slab and transverse to the axis of said blast; and a leading edge on said slots that is closer to the blast axis than the trailing edge, whereby said difference in edge level creates a turbulence that draws cool air from the slots to ow over the surface of the slab starting at said trailing edge.

2. A blast pad in accordance with claim l wherein the slab has edges and the slots extend to said exterior edges of the -slab and an air channel is provided along said exterior edges.

3. A blast pad in accordance with claim l wherein the slots extend to the edges of the slab, and a curbing is disposed over said slots on the top of said edges.

4. A blast pad in accordance with claim 1 wherein the depth of the slots is at least equal to their width.

5. A blast pad in accordance with claim 1 wherein the difference in level between the leading and trailing edges is at least one-eighth of the slot width.

6. A blast pad in accordance with claim 1 wherein the slab has exterior edges and the slots are deeper at the edges than toward the middle of the slab.

7. A self cooling blast pad for heat engines mounted at one end of the pad comprising: a slab disposed to intersect part of said blast; a plurality of slots in the surface of said slab and transverse to the axis of said blast; and a leading edge on said slots that is closer to the blast than the trailing edge, whereby said difference in edge level creates an aspiration that draws cool air from the slots to ow over the surface of the slab.

References Cited in the ile of this patent UNITED STATES PATENTS 2,685,936 Brenneman Aug. 10, 1954 2,706,013 Wigle Apr. 12, 1955 2,858,736 Hendrix Nov. 4, 1958 FOREIGN PATENTS 784,940 Great Britain Oct. 23, 1957 

